The development of an endoprosthesis for the metacarpophalangeal joint

Rheumatoid arthritis is a painful and debilitating disease which often afflicts the key joint of the hand, the metacarpophalangeal joint. In the worst cases the diseased joint has to be replaced with an artificial joint or prosthesis. The development of the Durham metacarpophalangeal prosthesis as it was taken from prototypes through to production samples, is described in this thesis. Testing of several Durham prostheses to over 70 million cycles has been carried out on a finger function simulator and consistent wear factors of the order of 0.4 x 10(^-) (^6)mm(^3)/Nm have been measured. These wear factors for the prosthesis were also significantly lower than any found previously. Production samples of the prosthesis have been manufactured together with appropriate surgical instrumentation. Tests of the prosthesis material, cross-linked polyethylene, rubbing against itself, have been undertaken on reciprocating pin on plate rigs and again show total wear factors of the order of 0.4 x lO(^-6)mm(^3)/Nm. Interestingly, it was found that pin wear was very much less than plate wear. The pin on plate tests were extended to include ultra-high molecular weight polyethylene (UHMWPE) rubbing against UHMWPE, as well as both polyethylenes against hard counterfaces and the results are reported. A new finger function simulator has been designed, manufactured and a validation test undertaken. Having written the necessary protocol, in conjunction with clinicians and the prosthesis manufacturer, ethical approval was obtained from the local research ethics committee and the Medical Devices Agency, to permit implantation of the prosthesis in human subjects. Lastly a hand strength measurement device for pre and post operation assessment of patients has been developed and manufactured

Methodology for Correlating Experimental and Finite Element Modal Analyses on Valve Trains

The widespread use of finite element models in assessing system dynamics for noise, vibration, and harshness (NVH) evaluation has led to recognition of the need for improved procedures for correlating models to experimental results. This study develops and applies a methodology to correlate an experimental modal analysis with a finite element modal analysis of valve trains in IC-engines. A pre-test analysis procedure is employed to guide the execution of tests used in the correlation process. This approach improves the efficiency of the test process, ensuring that the test article is neither under nor over-instrumented. The test-analysis model (TAM) that results from the pre-test simulation provides a means to compare the test and the model both during the experimental approach and during the model updating process. The validity of the correlation methodology is demonstrated through its application on the valve train of a single overhead cam (SOHC) engine

Panel options for large precision radio telescopes

The Cornell Caltech Atacama Telescope (CCAT) is a 25 m diameter telescope that will operate at wavelengths as short as 200 microns. CCAT will have active surface control to correct for gravitational and thermal distortions in the reflector support structure. The accuracy and stability of the reflector panels are critical to meeting the 10 micron HWFE (half wave front error) for the whole system. A system analysis based upon a versatile generic panel design has been developed and applied to numerous possible panel configurations. The error analysis includes the manufacturing errors plus the distortions from gravity, wind and thermal environment. The system performance as a function of panel size and construction material is presented. A compound panel approach is also described in which the reflecting surface is provided by tiles mounted on thermally stable and stiff sub-frames. This approach separates the function of providing an accurate reflecting surface from the requirement for a stable structure that is attached to the reflector support structure on three computer controlled actuators. The analysis indicates that there are several compound panel configurations that will easily meet the stringent CCAT requirements

A frequency domain approach to the analysis and optimization of valve spring dynamics

In this thesis a method is derived and presented, for the efficient analysis of the steady state response of dynamic systems with time variant propenies. The method is especially attractive for the simulation of the steady state response of lightly damped systems with low numbers of degree of freedom which are forced by a periodic excitation. A major feature of the method is that the system non-linearities can be successfully modelled as time variant propenies. An ideal application for this approach is the calculation of the dynamic response of a modal model for progressive valve springs in the frequency domain. The solution method is explained and derived using this example. The differences, drawbacks, and advantages are assessed by comparison with both a linear modal model and a discrete time-domain model; correlation with actual measurement is also shown. The extreme efficiency of the method allows its application in a more general study of the dynamic propenies of valve springs. This analysis is initially discussed and examined using statistical methods. Then the frequency domain solution method is employed to perform an automatic optimization of the spring frequency characteristic for a 16 valve prototype engine application. The spring design obtained from this study has been manufactured and the resulting hardware is discussed. The measured response of this hardware is compared with simulation results for the same configuration, verifying the fmdings from the statistical investigation and the optimization. Finally open issues and further envisaged work in the area of damping mechanisms in valve springs and manufacturing issues are diScussed and an approach for the next steps to take is outlined

A frequency domain approach to the analysis and optimization valve spring dynamics

In this thesis a method is derived and presented, for the efficient analysis of the steady state response of dynamic systems with time variant propenies. The method is especially attractive for the simulation of the steady state response of lightly damped systems with low numbers of degree of freedom which are forced by a periodic excitation. A major feature of the method is that the system non-linearities can be successfully modelled as time variant propenies. An ideal application for this approach is the calculation of the dynamic response of a modal model for progressive valve springs in the frequency domain. The solution method is explained and derived using this example. The differences, drawbacks, and advantages are assessed by comparison with both a linear modal model and a discrete time-domain model; correlation with actual measurement is also shown. The extreme efficiency of the method allows its application in a more general study of the dynamic propenies of valve springs. This analysis is initially discussed and examined using statistical methods. Then the frequency domain solution method is employed to perform an automatic optimization of the spring frequency characteristic for a 16 valve prototype engine application. The spring design obtained from this study has been manufactured and the resulting hardware is discussed. The measured response of this hardware is compared with simulation results for the same configuration, verifying the fmdings from the statistical investigation and the optimization. Finally open issues and further envisaged work in the area of damping mechanisms in valve springs and manufacturing issues are diScussed and an approach for the next steps to take is outlined

DESIGN OF A MULTI-DIRECTIONAL VARIABLE STIFFNESS LEG FOR DYNAMIC RUNNING

Recent developments in dynamic legged locomotion have focused on encoding a substantial component of leg intelligence into passive compliant mechanisms. One of the limitations of this approach is reduced adaptability: the final leg mechanism usually performs optimally for a small range of conditions (i.e. a certain robot weight, terrain, speed, gait, and so forth). For many situations in which a small locomotion system experiences a change in any of these conditions, it is desirable to have a variable stiffness leg to tune the natural frequency of the system for effective gait control. In this paper, we present an overview of variable stiffness leg spring designs, and introduce a new approach specifically for autonomous dynamic legged locomotion. We introduce a simple leg model that captures the spatial compliance of the tunable leg in three dimensions. Lastly, we present the design and manufacture of the multi-directional variable stiffness legs, and experimentally validate their correspondence to the proposed model